STM32F401CCU PCM5102A Sample Rate deviation

ADado.1 · ‎2022-07-27

Hi All, I'm using an STM32F401CCU with a TI PCM5102A DAC. I've set up a simple DMA (code attached) and a naïve square wave function. My issue is that the generated square wave is at the 'wrong' frequency. In the code I am generating a 440 hz (or multiple) square wave at a sample rate of 32khz (set in the I2S section of the IOC).

I am using an accumulator to either set a double variable to low or high whether it is above or below 0.5. This value is then multiplied by 32767 and then added to an entry in a signed 16 bit array.

I2S peripheral clock is at 128 MHZ. I seem to be getting however around 374Hz indicating perhaps that the time increment isn't correct (and then the sample rate is not) any help much appreciated, am new to this

/* USER CODE BEGIN Header */
/**
  ******************************************************************************
  * @file           : main.c
  * @brief          : Main program body
  ******************************************************************************
  * @attention
  *
  * Copyright (c) 2022 STMicroelectronics.
  * All rights reserved.
  *
  * This software is licensed under terms that can be found in the LICENSE file
  * in the root directory of this software component.
  * If no LICENSE file comes with this software, it is provided AS-IS.
  *
  ******************************************************************************
  */
/* USER CODE END Header */
/* Includes ------------------------------------------------------------------*/
#include "main.h"
 
/* Private includes ----------------------------------------------------------*/
/* USER CODE BEGIN Includes */
#include "math.h"
/* USER CODE END Includes */
 
/* Private typedef -----------------------------------------------------------*/
/* USER CODE BEGIN PTD */
 
/* USER CODE END PTD */
 
/* Private define ------------------------------------------------------------*/
/* USER CODE BEGIN PD */
 
 
#define SAMPLE_RATE 32000
 
 
 
 
 
 
/* USER CODE END PD */
 
/* Private macro -------------------------------------------------------------*/
/* USER CODE BEGIN PM */
 
/* USER CODE END PM */
 
/* Private variables ---------------------------------------------------------*/
I2S_HandleTypeDef hi2s3;
DMA_HandleTypeDef hdma_spi3_tx;
 
/* USER CODE BEGIN PV */
int16_t splx[16];
 
 
int16_t sample;
 
double T;
double Ts = 0.00003125;
/* USER CODE END PV */
 
/* Private function prototypes -----------------------------------------------*/
void SystemClock_Config(void);
static void MX_GPIO_Init(void);
static void MX_I2S3_Init(void);
static void MX_DMA_Init(void);
/* USER CODE BEGIN PFP */
 
/* USER CODE END PFP */
 
/* Private user code ---------------------------------------------------------*/
/* USER CODE BEGIN 0 */
 
/* USER CODE END 0 */
 
/**
  * @brief  The application entry point.
  * @retval int
  */
int main(void)
{
  /* USER CODE BEGIN 1 */
 
  /* USER CODE END 1 */
 
  /* MCU Configuration--------------------------------------------------------*/
 
  /* Reset of all peripherals, Initializes the Flash interface and the Systick. */
  HAL_Init();
 
  /* USER CODE BEGIN Init */
 
  /* USER CODE END Init */
 
  /* Configure the system clock */
  SystemClock_Config();
 
  /* USER CODE BEGIN SysInit */
 
  /* USER CODE END SysInit */
 
  /* Initialize all configured peripherals */
  MX_GPIO_Init();
  MX_DMA_Init();
  MX_I2S3_Init();
 
  /* USER CODE BEGIN 2 */
 
HAL_I2S_Transmit_DMA(&hi2s3, (uint16_t*)splx,8);
 
  /* USER CODE END 2 */
 
  /* Infinite loop */
  /* USER CODE BEGIN WHILE */
  while (1)
  {
    /* USER CODE END WHILE */
 
    /* USER CODE BEGIN 3 */
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  }
 
 
  /* USER CODE END 3 */
}
 
/**
  * @brief System Clock Configuration
  * @retval None
  */
void SystemClock_Config(void)
{
  RCC_OscInitTypeDef RCC_OscInitStruct = {0};
  RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};
 
  /** Macro to configure the PLL multiplication factor
  */
  __HAL_RCC_PLL_PLLM_CONFIG(8);
  /** Macro to configure the PLL clock source
  */
  __HAL_RCC_PLL_PLLSOURCE_CONFIG(RCC_PLLSOURCE_HSI);
  /** Configure the main internal regulator output voltage
  */
  __HAL_RCC_PWR_CLK_ENABLE();
  __HAL_PWR_VOLTAGESCALING_CONFIG(PWR_REGULATOR_VOLTAGE_SCALE2);
  /** Initializes the RCC Oscillators according to the specified parameters
  * in the RCC_OscInitTypeDef structure.
  */
  RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI;
  RCC_OscInitStruct.HSIState = RCC_HSI_ON;
  RCC_OscInitStruct.HSICalibrationValue = RCC_HSICALIBRATION_DEFAULT;
  RCC_OscInitStruct.PLL.PLLState = RCC_PLL_NONE;
  RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSI;
  if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
  {
    Error_Handler();
  }
  /** Initializes the CPU, AHB and APB buses clocks
  */
  RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
                              |RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
  RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_HSI;
  RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
  RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV1;
  RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;
 
  if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_0) != HAL_OK)
  {
    Error_Handler();
  }
}
 
/**
  * @brief I2S3 Initialization Function
  * @param None
  * @retval None
  */
static void MX_I2S3_Init(void)
{
 
  /* USER CODE BEGIN I2S3_Init 0 */
 
  /* USER CODE END I2S3_Init 0 */
 
  /* USER CODE BEGIN I2S3_Init 1 */
 
  /* USER CODE END I2S3_Init 1 */
  hi2s3.Instance = SPI3;
  hi2s3.Init.Mode = I2S_MODE_MASTER_TX;
  hi2s3.Init.Standard = I2S_STANDARD_PHILIPS;
  hi2s3.Init.DataFormat = I2S_DATAFORMAT_16B;
  hi2s3.Init.MCLKOutput = I2S_MCLKOUTPUT_DISABLE;
  hi2s3.Init.AudioFreq = I2S_AUDIOFREQ_32K;
  hi2s3.Init.CPOL = I2S_CPOL_LOW;
  hi2s3.Init.ClockSource = I2S_CLOCK_PLL;
  hi2s3.Init.FullDuplexMode = I2S_FULLDUPLEXMODE_ENABLE;
  if (HAL_I2S_Init(&hi2s3) != HAL_OK)
  {
    Error_Handler();
  }
  /* USER CODE BEGIN I2S3_Init 2 */
 
  /* USER CODE END I2S3_Init 2 */
 
}
 
/**
  * Enable DMA controller clock
  */
static void MX_DMA_Init(void)
{
 
  /* DMA controller clock enable */
  __HAL_RCC_DMA1_CLK_ENABLE();
 
  /* DMA interrupt init */
  /* DMA1_Stream5_IRQn interrupt configuration */
  HAL_NVIC_SetPriority(DMA1_Stream5_IRQn, 0, 0);
  HAL_NVIC_EnableIRQ(DMA1_Stream5_IRQn);
 
}
 
/**
  * @brief GPIO Initialization Function
  * @param None
  * @retval None
  */
static void MX_GPIO_Init(void)
{
 
  /* GPIO Ports Clock Enable */
  __HAL_RCC_GPIOC_CLK_ENABLE();
  __HAL_RCC_GPIOH_CLK_ENABLE();
  __HAL_RCC_GPIOA_CLK_ENABLE();
  __HAL_RCC_GPIOB_CLK_ENABLE();
 
}
 
/* USER CODE BEGIN 4 */
int16_t outputBuffer(){
 
#define TWOPI 6.28318530718
 
 
 
double sampledouble = 0;
 
 
T = T + (Ts*440);
if (T >= 1.0){
 
	T = 0;
}
 
 
 
 
if (T < 0.5){
 
	sampledouble = -0.8;
}
 
 
if (T >= 0.5){
 
	sampledouble = 0.8;
}
 
 
 
//Normalise
 
 
 
sample = sampledouble * 32767;
return sample;
 
}
 
 
 
 
void HAL_I2S_TxHalfCpltCallback (I2S_HandleTypeDef * hi2s){
 
 
 
splx[0] = outputBuffer();
splx[1] = splx[0];
splx[2] = outputBuffer();
splx[3] = splx[2];
splx[4] = outputBuffer();
splx[5] = splx[4];
splx[6] = outputBuffer();
splx[7] = splx[6];
 
 
}
 
 
 
void HAL_I2S_TxCpltCallback (I2S_HandleTypeDef * hi2s){
 
 
 
	splx[8] = outputBuffer();
	splx[9] = splx[8];
	splx[10]= outputBuffer();
	splx[11]=splx[10];
	splx[12]=outputBuffer();
	splx[13]= splx[12];
	splx[14]= outputBuffer();
	splx[15]= splx[14];
 
 
 
 
 
 
 
 
}
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
/* USER CODE END 4 */
 
/**
  * @brief  This function is executed in case of error occurrence.
  * @retval None
  */
void Error_Handler(void)
{
  /* USER CODE BEGIN Error_Handler_Debug */
  /* User can add his own implementation to report the HAL error return state */
  __disable_irq();
  while (1)
  {
  }
  /* USER CODE END Error_Handler_Debug */
}
 
#ifdef  USE_FULL_ASSERT
/**
  * @brief  Reports the name of the source file and the source line number
  *         where the assert_param error has occurred.
  * @param  file: pointer to the source file name
  * @param  line: assert_param error line source number
  * @retval None
  */
void assert_failed(uint8_t *file, uint32_t line)
{
  /* USER CODE BEGIN 6 */
  /* User can add his own implementation to report the file name and line number,
     ex: printf("Wrong parameters value: file %s on line %d\r\n", file, line) */
  /* USER CODE END 6 */
}
#endif /* USE_FULL_ASSERT */

Piranha · ‎2022-07-27

Format the code sanely, edit out all the junk and post only the relevant code in forum.

The square wave period is: 32000 / 440 = 73 samples. Toggle the value +/-32767 for every 36 samples and that's it. Or a 36/37 samples to get closer to the exact frequency. It's a basic math!

ADado.1 · ‎2022-07-27

Not really helpful. My math is fine, I've described what the problem is and it's not to do with the methodology around generating a square wave. Not sure if you're showing off or something

Piranha · ‎2022-07-27

> I2S peripheral clock is at 128 MHZ.

~~Not possible with HSI as a SYSCLK source.~~ And your MCU has a maximum frequency of 84 MHz. You are clicking CubeMX and that tool shows clocks with a plain numbers in GUI interface even for those, who don't read the documentation!

P.S. You do understand that Cortex-M4 has a single precision FPU and therefore your double type variables are calculated in software with a relatively heavy processing?

ADado.1 · ‎2022-07-27

The PLL is generating it from the HSI

Piranha · ‎2022-07-27

OK, indeed it seems to be possible. Anyway double-check if there are no some additional limitations for APB/I2S clock ratio.

And read and check the actual registers for all the clocks, especially the dividers, which are calculated from the I2S_AUDIOFREQ_32K setting. ST's code cannot be trusted on anything...

ADado.1 · ‎2022-07-27

Thanks a lot, will do!